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S_CLIENT(1)			    OpenSSL			   S_CLIENT(1)

NAME
       s_client	- SSL/TLS client program

SYNOPSIS
       openssl s_client	[-help]	[-connect host:port] [-proxy host:port]	[-unix
       path] [-4] [-6] [-servername name] [-verify depth]
       [-verify_return_error] [-cert filename] [-certform DER|PEM] [-key
       filename] [-keyform DER|PEM] [-pass arg]	[-CApath directory] [-CAfile
       filename] [-no-CAfile] [-no-CApath] [-dane_tlsa_domain domain]
       [-dane_tlsa_rrdata rrdata] [-dane_ee_no_namechecks] [-attime timestamp]
       [-check_ss_sig] [-crl_check] [-crl_check_all] [-explicit_policy]
       [-extended_crl] [-ignore_critical] [-inhibit_any] [-inhibit_map]
       [-no_check_time]	[-partial_chain] [-policy arg] [-policy_check]
       [-policy_print] [-purpose purpose] [-suiteB_128]	[-suiteB_128_only]
       [-suiteB_192] [-trusted_first] [-no_alt_chains] [-use_deltas]
       [-auth_level num] [-verify_depth	num] [-verify_email email]
       [-verify_hostname hostname] [-verify_ip ip] [-verify_name name]
       [-x509_strict] [-reconnect] [-showcerts]	[-debug] [-msg]	[-nbio_test]
       [-state]	[-nbio]	[-crlf]	[-ign_eof] [-no_ign_eof] [-quiet] [-ssl3]
       [-tls1] [-tls1_1] [-tls1_2] [-no_ssl3] [-no_tls1] [-no_tls1_1]
       [-no_tls1_2] [-dtls] [-dtls1] [-dtls1_2]	[-fallback_scsv] [-async]
       [-split_send_frag] [-max_pipelines] [-read_buf] [-bugs] [-comp]
       [-no_comp] [-sigalgs sigalglist]	[-curves curvelist] [-cipher
       cipherlist] [-serverpref] [-starttls protocol] [-xmpphost hostname]
       [-engine	id] [-tlsextdebug] [-no_ticket]	[-sess_out filename] [-sess_in
       filename] [-rand	file(s)] [-serverinfo types] [-status] [-alpn
       protocols] [-nextprotoneg protocols] [-ct|noct] [-ctlogfile]

DESCRIPTION
       The s_client command implements a generic SSL/TLS client	which connects
       to a remote host	using SSL/TLS. It is a very useful diagnostic tool for
       SSL servers.

OPTIONS
       In addition to the options below	the s_client utility also supports the
       common and client only options documented in the	in the "Supported
       Command Line Commands" section of the SSL_CONF_cmd(3) manual page.

       -help
	   Print out a usage message.

       -connect	host:port
	   This	specifies the host and optional	port to	connect	to. If not
	   specified then an attempt is	made to	connect	to the local host on
	   port	4433.

       -proxy host:port
	   When	used with the -connect flag, the program uses the host and
	   port	specified with this flag and issues an HTTP CONNECT command to
	   connect to the desired server.

       -unix path
	   Connect over	the specified Unix-domain socket.

       -4  Use IPv4 only.

       -6  Use IPv6 only.

       -servername name
	   Set the TLS SNI (Server Name	Indication) extension in the
	   ClientHello message.

       -cert certname
	   The certificate to use, if one is requested by the server. The
	   default is not to use a certificate.

       -certform format
	   The certificate format to use: DER or PEM. PEM is the default.

       -key keyfile
	   The private key to use. If not specified then the certificate file
	   will	be used.

       -keyform	format
	   The private format to use: DER or PEM. PEM is the default.

       -pass arg
	   the private key password source. For	more information about the
	   format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).

       -verify depth
	   The verify depth to use. This specifies the maximum length of the
	   server certificate chain and	turns on server	certificate
	   verification.  Currently the	verify operation continues after
	   errors so all the problems with a certificate chain can be seen. As
	   a side effect the connection	will never fail	due to a server
	   certificate verify failure.

       -verify_return_error
	   Return verification errors instead of continuing. This will
	   typically abort the handshake with a	fatal error.

       -CApath directory
	   The directory to use	for server certificate verification. This
	   directory must be in	"hash format", see verify for more
	   information.	These are also used when building the client
	   certificate chain.

       -CAfile file
	   A file containing trusted certificates to use during	server
	   authentication and to use when attempting to	build the client
	   certificate chain.

       -no-CAfile
	   Do not load the trusted CA certificates from	the default file
	   location

       -no-CApath
	   Do not load the trusted CA certificates from	the default directory
	   location

       -dane_tlsa_domain domain
	   Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
	   TLSA	base domain which becomes the default SNI hint and the primary
	   reference identifier	for hostname checks.  This must	be used	in
	   combination with at least one instance of the -dane_tlsa_rrdata
	   option below.

	   When	DANE authentication succeeds, the diagnostic output will
	   include the lowest (closest to 0) depth at which a TLSA record
	   authenticated a chain certificate.  When that TLSA record is	a "2 1
	   0" trust anchor public key that signed (rather than matched)	the
	   top-most certificate	of the chain, the result is reported as	"TA
	   public key verified".  Otherwise, either the	TLSA record "matched
	   TA certificate" at a	positive depth or else "matched	EE
	   certificate"	at depth 0.

       -dane_tlsa_rrdata rrdata
	   Use one or more times to specify the	RRDATA fields of the DANE TLSA
	   RRset associated with the target service.  The rrdata value is
	   specied in "presentation form", that	is four	whitespace separated
	   fields that specify the usage, selector, matching type and
	   associated data, with the last of these encoded in hexadecimal.
	   Optional whitespace is ignored in the associated data field.	 For
	   example:

	     $ openssl s_client	-brief -starttls smtp \
	       -connect	smtp.example.com:25 \
	       -dane_tlsa_domain smtp.example.com \
	       -dane_tlsa_rrdata "2 1 1
		 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
	       -dane_tlsa_rrdata "2 1 1
		 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
	     ...
	     Verification: OK
	     Verified peername:	smtp.example.com
	     DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate	at depth 1
	     ...

       -dane_ee_no_namechecks
	   This	disables server	name checks when authenticating	via DANE-EE(3)
	   TLSA	records.  For some applications, primarily web browsers, it is
	   not safe to disable name checks due to "unknown key share" attacks,
	   in which a malicious	server can convince a client that a connection
	   to a	victim server is instead a secure connection to	the malicious
	   server.  The	malicious server may then be able to violate cross-
	   origin scripting restrictions.  Thus, despite the text of RFC7671,
	   name	checks are by default enabled for DANE-EE(3) TLSA records, and
	   can be disabled in applications where it is safe to do so.  In
	   particular, SMTP and	XMPP clients should set	this option as SRV and
	   MX records already make it possible for a remote domain to redirect
	   client connections to any server of its choice, and in any case
	   SMTP	and XMPP clients do not	execute	scripts	downloaded from	remote
	   servers.

       -attime,	-check_ss_sig, -crl_check, -crl_check_all, -explicit_policy,
       -extended_crl, -ignore_critical,	-inhibit_any, -inhibit_map,
       -no_alt_chains, -no_check_time, -partial_chain, -policy,	-policy_check,
       -policy_print, -purpose,	-suiteB_128, -suiteB_128_only, -suiteB_192,
       -trusted_first, -use_deltas, -auth_level, -verify_depth,	-verify_email,
       -verify_hostname, -verify_ip, -verify_name, -x509_strict
	   Set various certificate chain validation options. See the verify(1)
	   manual page for details.

       -reconnect
	   reconnects to the same server 5 times using the same	session	ID,
	   this	can be used as a test that session caching is working.

       -showcerts
	   display the whole server certificate	chain: normally	only the
	   server certificate itself is	displayed.

       -prexit
	   print session information when the program exits. This will always
	   attempt to print out	information even if the	connection fails.
	   Normally information	will only be printed out once if the
	   connection succeeds.	This option is useful because the cipher in
	   use may be renegotiated or the connection may fail because a	client
	   certificate is required or is requested only	after an attempt is
	   made	to access a certain URL. Note: the output produced by this
	   option is not always	accurate because a connection might never have
	   been	established.

       -state
	   prints out the SSL session states.

       -debug
	   print extensive debugging information including a hex dump of all
	   traffic.

       -msg
	   show	all protocol messages with hex dump.

       -trace
	   show	verbose	trace output of	protocol messages. OpenSSL needs to be
	   compiled with enable-ssl-trace for this option to work.

       -msgfile
	   file	to send	output of -msg or -trace to, default standard output.

       -nbio_test
	   tests non-blocking I/O

       -nbio
	   turns on non-blocking I/O

       -crlf
	   this	option translated a line feed from the terminal	into CR+LF as
	   required by some servers.

       -ign_eof
	   inhibit shutting down the connection	when end of file is reached in
	   the input.

       -quiet
	   inhibit printing of session and certificate information.  This
	   implicitly turns on -ign_eof	as well.

       -no_ign_eof
	   shut	down the connection when end of	file is	reached	in the input.
	   Can be used to override the implicit	-ign_eof after -quiet.

       -psk_identity identity
	   Use the PSK identity	identity when using a PSK cipher suite.

       -psk key
	   Use the PSK key key when using a PSK	cipher suite. The key is given
	   as a	hexadecimal number without leading 0x, for example -psk
	   1a2b3c4d.

       -ssl3, -tls1, -tls1_1, -tls1_2, -no_ssl3, -no_tls1, -no_tls1_1,
       -no_tls1_2
	   These options require or disable the	use of the specified SSL or
	   TLS protocols.  By default s_client will negotiate the highest
	   mutually supported protocol version.	 When a	specific TLS version
	   is required,	only that version will be offered to and accepted from
	   the server.

       -dtls, -dtls1, -dtls1_2
	   These options make s_client use DTLS	protocols instead of TLS.
	   With	-dtls, s_client	will negotiate any supported DTLS protocol
	   version, whilst -dtls1 and -dtls1_2 will only support DTLS1.0 and
	   DTLS1.2 respectively.

       -fallback_scsv
	   Send	TLS_FALLBACK_SCSV in the ClientHello.

       -async
	   switch on asynchronous mode.	Cryptographic operations will be
	   performed asynchronously. This will only have an effect if an
	   asynchronous	capable	engine is also used via	the -engine option.
	   For test purposes the dummy async engine (dasync) can be used (if
	   available).

       -split_send_frag	int
	   The size used to split data for encrypt pipelines. If more data is
	   written in one go than this value then it will be split into
	   multiple pipelines, up to the maximum number	of pipelines defined
	   by max_pipelines. This only has an effect if	a suitable ciphersuite
	   has been negotiated,	an engine that supports	pipelining has been
	   loaded, and max_pipelines is	greater	than 1.	See
	   SSL_CTX_set_split_send_fragment(3) for further information.

       -max_pipelines int
	   The maximum number of encrypt/decrypt pipelines to be used. This
	   will	only have an effect if an engine has been loaded that supports
	   pipelining (e.g. the	dasync engine) and a suitable ciphersuite has
	   been	negotiated. The	default	value is 1.  See
	   SSL_CTX_set_max_pipelines(3)	for further information.

       -read_buf int
	   The default read buffer size	to be used for connections. This will
	   only	have an	effect if the buffer size is larger than the size that
	   would otherwise be used and pipelining is in	use (see
	   SSL_CTX_set_default_read_buffer_len(3) for further information).

       -bugs
	   there are several known bug in SSL and TLS implementations. Adding
	   this	option enables various workarounds.

       -comp
	   Enables support for SSL/TLS compression.  This option was
	   introduced in OpenSSL 1.1.0.	 TLS compression is not	recommended
	   and is off by default as of OpenSSL 1.1.0.

       -no_comp
	   Disables support for	SSL/TLS	compression.  TLS compression is not
	   recommended and is off by default as	of OpenSSL 1.1.0.

       -brief
	   only	provide	a brief	summary	of connection parameters instead of
	   the normal verbose output.

       -sigalgs	sigalglist
	   Specifies the list of signature algorithms that are sent by the
	   client.  The	server selects one entry in the	list based on its
	   preferences.	 For example strings, see SSL_CTX_set1_sigalgs(3)

       -curves curvelist
	   Specifies the list of supported curves to be	sent by	the client.
	   The curve is	is ultimately selected by the server. For a list of
	   all curves, use:

	       $ openssl ecparam -list_curves

       -cipher cipherlist
	   this	allows the cipher list sent by the client to be	modified.
	   Although the	server determines which	cipher suite is	used it	should
	   take	the first supported cipher in the list sent by the client. See
	   the ciphers command for more	information.

       -starttls protocol
	   send	the protocol-specific message(s) to switch to TLS for
	   communication.  protocol is a keyword for the intended protocol.
	   Currently, the only supported keywords are "smtp", "pop3", "imap",
	   "ftp", "xmpp", "xmpp-server", and "irc."

       -xmpphost hostname
	   This	option,	when used with "-starttls xmpp"	or "-starttls xmpp-
	   server", specifies the host for the "to" attribute of the stream
	   element.  If	this option is not specified, then the host specified
	   with	"-connect" will	be used.

       -tlsextdebug
	   print out a hex dump	of any TLS extensions received from the
	   server.

       -no_ticket
	   disable RFC4507bis session ticket support.

       -sess_out filename
	   output SSL session to filename

       -sess_in	sess.pem
	   load	SSL session from filename. The client will attempt to resume a
	   connection from this	session.

       -engine id
	   specifying an engine	(by its	unique id string) will cause s_client
	   to attempt to obtain	a functional reference to the specified
	   engine, thus	initialising it	if needed. The engine will then	be set
	   as the default for all available algorithms.

       -rand file(s)
	   a file or files containing random data used to seed the random
	   number generator, or	an EGD socket (see RAND_egd(3)).  Multiple
	   files can be	specified separated by an OS-dependent character.  The
	   separator is	; for MS-Windows, , for	OpenVMS, and : for all others.

       -serverinfo types
	   a list of comma-separated TLS Extension Types (numbers between 0
	   and 65535).	Each type will be sent as an empty ClientHello TLS
	   Extension.  The server's response (if any) will be encoded and
	   displayed as	a PEM file.

       -status
	   sends a certificate status request to the server (OCSP stapling).
	   The server response (if any)	is printed out.

       -alpn protocols,	-nextprotoneg protocols
	   these flags enable the Enable the Application-Layer Protocol
	   Negotiation or Next Protocol	Negotiation extension, respectively.
	   ALPN	is the IETF standard and replaces NPN.	The protocols list is
	   a comma-separated protocol names that the client should advertise
	   support for.	The list should	contain	most wanted protocols first.
	   Protocol names are printable	ASCII strings, for example "http/1.1"
	   or "spdy/3".	 Empty list of protocols is treated specially and will
	   cause the client to advertise support for the TLS extension but
	   disconnect just after receiving ServerHello with a list of server
	   supported protocols.

       -ct|noct
	   Use one of these two	options	to control whether Certificate
	   Transparency	(CT) is	enabled	(-ct) or disabled (-noct).  If CT is
	   enabled, signed certificate timestamps (SCTs) will be requested
	   from	the server and reported	at handshake completion.

	   Enabling CT also enables OCSP stapling, as this is one possible
	   delivery method for SCTs.

       -ctlogfile
	   A file containing a list of known Certificate Transparency logs.
	   See SSL_CTX_set_ctlog_list_file(3) for the expected file format.

CONNECTED COMMANDS
       If a connection is established with an SSL server then any data
       received	from the server	is displayed and any key presses will be sent
       to the server. When used	interactively (which means neither -quiet nor
       -ign_eof	have been given), the session will be renegotiated if the line
       begins with an R, and if	the line begins	with a Q or if end of file is
       reached,	the connection will be closed down.

NOTES
       s_client	can be used to debug SSL servers. To connect to	an SSL HTTP
       server the command:

	openssl	s_client -connect servername:443

       would typically be used (https uses port	443). If the connection
       succeeds	then an	HTTP command can be given such as "GET /" to retrieve
       a web page.

       If the handshake	fails then there are several possible causes, if it is
       nothing obvious like no client certificate then the -bugs, -ssl3,
       -tls1, -no_ssl3,	-no_tls1 options can be	tried in case it is a buggy
       server. In particular you should	play with these	options	before
       submitting a bug	report to an OpenSSL mailing list.

       A frequent problem when attempting to get client	certificates working
       is that a web client complains it has no	certificates or	gives an empty
       list to choose from. This is normally because the server	is not sending
       the clients certificate authority in its	"acceptable CA list" when it
       requests	a certificate. By using	s_client the CA	list can be viewed and
       checked.	However	some servers only request client authentication	after
       a specific URL is requested. To obtain the list in this case it is
       necessary to use	the -prexit option and send an HTTP request for	an
       appropriate page.

       If a certificate	is specified on	the command line using the -cert
       option it will not be used unless the server specifically requests a
       client certificate. Therefor merely including a client certificate on
       the command line	is no guarantee	that the certificate works.

       If there	are problems verifying a server	certificate then the
       -showcerts option can be	used to	show the whole chain.

       The s_client utility is a test tool and is designed to continue the
       handshake after any certificate verification errors. As a result	it
       will accept any certificate chain (trusted or not) sent by the peer.
       None test applications should not do this as it makes them vulnerable
       to a MITM attack. This behaviour	can be changed by with the
       -verify_return_error option: any	verify errors are then returned
       aborting	the handshake.

BUGS
       Because this program has	a lot of options and also because some of the
       techniques used are rather old, the C source of s_client	is rather hard
       to read and not a model of how things should be done.  A	typical	SSL
       client program would be much simpler.

       The -prexit option is a bit of a	hack. We should	really report
       information whenever a session is renegotiated.

SEE ALSO
       SSL_CONF_cmd(3),	sess_id(1), s_server(1), ciphers(1)

HISTORY
       The -no_alt_chains options was first added to OpenSSL 1.1.0.

COPYRIGHT
       Copyright 2000-2016 The OpenSSL Project Authors.	All Rights Reserved.

       Licensed	under the OpenSSL license (the "License").  You	may not	use
       this file except	in compliance with the License.	 You can obtain	a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.

1.1.0f				  2017-05-25			   S_CLIENT(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CONNECTED COMMANDS | NOTES | BUGS | SEE ALSO | HISTORY | COPYRIGHT

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